Histograms

As a test, I made up an under 100k jpg of a typical pre-restoration image. I made a histogram of that jpg. Then I uploaded the image jpg and viewed it. Then I saved it (not via copy) and ran another histogram. Attached are my results.

I use a PC, though I can't imagine how that could make a difference. There is no mechanism to change the file during or after uploading, or during downloading. If anything did get changed, the file would be corrupted and unviewable. It's a straight binary transfer.

What DJ said is true. That's why I don't rely on historgrams anymore. If I want to see what's going on in the image. I look in the channels itself. Being a curve user only. A lot of people that use levels that go to using curves would like to see a historgram with curves, like in using levels. But really, I would not worry, because what you see on the screen is what you see on the downloaded image is what counts(as in the downloaded images). I have that Dan Margulis attitude. Do you want good looking images or good looking historgrams. Even if your not into Dan Margulis, Katrin Eismann has it in her book as an example: page 47 and 48. The before and after images, the historgrams (one in 8 bit and the other in 16 bit) are the same. After changes done to it. The images look the same in 8 and 16 bit, but the historgrams are different.

This looks like JPG compression to me---throwing out data that is not needed to maintain visual coherency. Are you sure you aren't comparing the histograms from your original file and the post-compression JPG?

What's the file size difference between the JPG you create and the one you download?

(BTW, that's a fantastic restoration, I follow all your posts with a sense of urgency)

Thank you every one for trying to help me unravel this mystery. You kept asking me questions which made ma keep going back over what I had done.

I was certainly taking the histogram from the compressed image before I sent it and comparing it to the image I downloaded. There was so much tone drop out I just couldn’t work with the images.

Finally I’ve worked out what I was doing. Because I can’t sit at all I work while standing at the computer and that needs to be for short periods. I.e. I save my work and come back to it many times. A bad thing to do with JPEG.

What I was doing was saving in bitmap because that was the only option available. I now find I can save in JPEG, open in PhotoShop and save as TIFF. The problem was accruing when I saved as bitmap.

Thanks for the information on curves but I just can’t get the hang of them. I live on a farm miles from anywhere I couldn’t go to Photoshop classes if they even existed. At 63 my learning curve is pretty lousy!!!!

Sally, I quite agree with Kaulike -- your experience and knowledge as a retoucher and your current level of knowledge of Photoshop translate into excellence in your work -- whether you know a particular method or not. The end result is what counts.

If there are any techniques that would speed up your work, since you have to stand to work, I guess those would be helpful to learn. I avoided learning keystroke shortcuts for years, but have to admit that they do save time. Curves continue to be a problem for me -- I can screw an image up faster using curves than any other technique -- but I'm gonna learn to use them someday! :p